Method and means of magnetic recording and reproducing sound



May 5, 1953 l.. H. coNNELL 2,637,561

METHOD AND MEANS oF MAGNETIC RECORD-ING AND RDPRoDucING souND INVENTDR. LAWRENCE H. CoNNnLL I9 7' TORNEYS May 5, 1953 L. H. coNNELl.- 2,637,561

METHOD AND MEANS DE MAGNETIC RECORDING AND REPRODUCING souND Filed Feb. 8. 1947 2 SHEETS-SHEET 2 IN VENTOR. LAWRENCE H. CoNNELL @Ml d @mi -obaeet ef the invent Patented May 5, 1953 `JINI-ITID :STATES PATENT OFFICE ,actuel 'METHOD AND fMiiANs for MAGNETIC Rs- -connING AND REPR'ODUCING SOUND 'Lawrence Connell, Detroit, Mich. aspri-@atten February s, 194'7, serial No. 727,424

'recording member has been passed in uhsup portee relatively free conditioning' the 'magnetic 'sensitive -head which is either `operatine to iin press magnetic variations in the 'member or to `pick up "such magneticvariations ror the epiduction thereof into/distinguishable sounds. The sensitive magnene nea-d nas hereteiere seeratee in magnetic relation 'to a 'free section oi `'the recording 'rne'fnber moving between an unwinding device or reel and a winding' device or ree-1. Ai- 'though 'satisfactory magnetic recordings amrre-v productions have been made by rsuch neviees,

there has been present objectionabie'noises and :discards in "the reprodueton of the sound earned on the siagne-uned recording member. "These undesirable noises 'have inane 'wirereeording and reproducing rsyste'zrrs oi this character earn-pare recording and reproducing systems.

i have vdisarmere'd that `scnrree of 'siren "obi jti'nab'l noises and discords is the recurrent and/or variable frequency of 'snie'nn-fiinii'orin part or parts of the apparatus falling withinfthe niseordantrange and that particularly onesource er such noise is'due to the eiastieity of the reteni-k ihediu-incausihg ninu'te elongation and ecn#- tracnontnereei as it passes in magnetic relation to the head. I have 'iind that if the 'eioh'gatiii contraction oi thatpor'tion oi the recording iheln'ber immediately -beiore and immediately ltiterthe head 'is `subst'antially dampen out, in'st if 'not all the discordant noi-ses heretofore prevalentie such apparatus is ier h praticai purposes lsubstanti-ally eiiininatedfroin the reproduced sou-nd and 'the tone quality is censider 'abiy improved.

'important object of this lin'vwention 'is 'te f vin ei inermi @fr anarneans for nase a 'reeer' ne in nner and ier rnagrietieauy repruueing sound vwe es from 'a record-ing hieinber `ivhie'h siibstai ially e1irhi- Sites an ebieenenabie noise" and enseres here re eeirring in s. `Ai-nrtlierini 'is novel mechanism for advancing "t ana-1 'eine-ganen /or contraction of that portion of the recording r'nember passing through the head. A urthe'r important object of the invention is to provide apparatus for accomplishing this purpose which is inexpensive to manufacture and assemble and which can be incorporated on existing devices lof this character without appreciable alteration in design.

Various other objects, advantages rand meritorious features oi the invention will become more ully apparent from the following specification, appended claim and accompanying drawings wherein:

Fig. 1 is a side elevation of an apparatus embodying the features of the invention, y g

YFig. 2 is a top plan View of the apparatus 'of Fig. 1,

Fig. 3 is a detail sectional view along line 3 3 of Fig. 1, l

Fig. 4 is an enlarged detail vertical sectional view along line 4-4 of Fig. 1,

Fig. 5 is a lnodiiication of the invention sche matically illustrating another manner 0f accomlplishing the objects of the invention, and

Fig. 6 is an enlarged detail sectional view along line 6--6 of Fig, v5.

Discord is a phenomenon of beats, and lit Yis Well understood by those skilled in the art that approximately 30 beats per second produce the worst or most undesirable discord, and that fewer than five `and more than 60 beats per second are usuallyy outside of the discord producing range.

l.'[n Vdiscovering the lreason for the production of minute, nevertheless mainly operates at a frequency which itself is Within the discordant range or which heterodynes against the musi-cal frequency to produce a frequency in 1this range and heretofore superimposed its undesired tones either upon the `recording medium when .the sound waves were magnetically recorded thereon or in there'production of Vsound waves by a magnetically responsive reproducing head. The 'elastical-stretching and `contraction of vthe recording member' apparently rresults either from some non'- uniformity of the speed of the driving and guiding members of the apparatus or non-uniformity of friction between the guiding members and the recording medium.

It is the common practice as hereinabove mentioned to run the wire from a reel onto a constant sneed reel or around a constant speed capstan. The magnetic device or sound head which either impresses magnetic variations on the wire or is influenced bv the magnetic variations therein has been located in the past between the take-olf reel and the winding reel if a capstan is omitted. A change in tension in the wire, which may be caused by non-uniformity in the speed or friction of one or more parts of the apparatus or by the vibration of the wire itself. will produce a change in length of the wire. The extent of the change in length of the wire will depend upon a number of factors such as the degree of change in tension, the elective length of the wire, the modulus of elasticity of the wire, and the crosssectional area of the wire. Since the wire is not rigidly held but passes on and oiT various members of the apparatus in its travel, the limits of its effective length are not readily ascertainable. However, for illustrative purposes, the eilective length can be considered as the distance between the point of contact with the head and either the point of contact with the constant speed capstan or constant speed reel which ever is employed.

The change in length of a wire member can be represented by the formula:

where AD is the change in length, A is the crosssectional area, L is the effective length, E is the modulus of elasticity of the material of the wire, and P the axial load on the wire. In an inchpound ratio, A may be measured in square inches, L in linear inches, E in pounds per square inch and P in pounds. Ii P and L can be lowered it is evident that the change in length of the wire can be reduced. A and E are relatively constant factors concerning the material of the'wire and assuming a standard type of recording wire is employed cannot normally be altered. The change in P can be reduced by introducing low inertia constant tension devices and by lubrication between the wire and the sound head. L can be reduced by more compact assembly of parts. A11 this assumes that the moving parts are operated at constant speed and in synchronism. Any nonuniformity in the velocity controlling and guiding parts of the apparatus will impose a tension on the wire which will produce a vibratory elongation and contraction of the wire and cause a discordant noise to be reproduced.

Various experimental arrangements have produced beneficial results. I have found that moving the sound head closer to the capstan or toward either one of the reels reduces the discordant noises. Better results were obtained by the provision of one or more low inertia constant tension devices through which the recording medium was fed.

An example of an apparatus employing such low inertia means is schematically illustrated in Figs. 5 and 6. The recording medium which in this instance is the .steel plated wire I!) is unwound from one reel I2 and simultaneously wound upon a second reel I4 spaced therefrom; Approximately mid-way between the two reels the wire passed through the magnetic neld of a magnetically sensitive head generally indicated at I6 which may either serve to impress magnetic variations on the wire or pick up such variations and control the reproduction of sound waves in the apparatus.

Without the provision of any means for preventing the elongation and contraction of the wire, the usual discordant and objectionable noises were reproduced. To dampen and thereby substantially prevent such elongation and contraction of the recording wire, I provided on opposite sides of the sound head and between the the same and the reels means in the form of low inertia spring devices which considerably helped to reduce changes in tension of the wire portion passing in the vicinity of and through the sound head. One such device indicated at I3 is positioned between the take-off reel I2 and the head, and the other device indicated at 20 is positioned between the head and the take-on reel I4.

It is preferred to construct each device I8 and 20 so that it will act with the lowest possible inertia on the wire to substantially eliminate any change in the tension of the wire.. To satis.- factorily accomplish this purpose, the device will move with the wire rather than let the tension of the wire change. Shown in Fig. 6 is one example of a low inertia device for this object. It comprises a base 22 of wood or the like disposed off to one side of the wire. Secured to the tip of the base is one end of a thin flexible member 24 preferably formed of metal which projects laterally therefrom. The free end of the member is bent upon itself into the form of a U to provide an end section 26 thereof extending parallel to the major length of the member. Interposed between the bent section 2S and the opposite portion of the member is a mass of cushioning material such as felt. Preferably, two similar pads of felt indicated at 28-28 are used which are lightly compressed together on opposite sides of the recording wire I0. v

As shown in Fig. 5, the padded free end of th member 24 of each device is disposed offset to the plane common to the operating end of the sound head and the peripheral portion of either reel from or upon which the wire is led. This causes the wire to detour slightly out of the plane between each reel and the sound head as is evident in Fig. 5. Each device I8 or 20 may be d isposed slightly above the plane as shown in Fig. 5 or slightly therebelow. v

In operation, the recording wire runs smoothly through the felt pads of each device. Any vibratory motions set up in the wire as it leaves the reel I2 or feeds on the reel I4 is substantially damped out by the devices so that the section of wire between the two devices travels without any vibration. If any non-uniformity of speed or friction in the moving parts of the apparatus occur,-a tension will be imposed on the recording Wire tending to stretch or extend its length. In such an event either one or both the flexible members 24 of the two dampening devices I8 and 20 Will yield or flex to the force, such as by bending toward the straight line position of the wire between each reel and the sound head. When the tension is eased the members 24 will return to their initial operation position. In this manner any change in tension which would other- Wise stretch the section of the wire in the vicinity of the sound head will be substantially eliminated or at least conned to the sections of the wire remote from the head. y y

The preferred apparatus for accomplishing the objects ofjthe invention is illustrated in Figs 1 to 4 inclusive, The recording member or wire iin this instance is `:supported :'along'lthat'rsectioh @of the length .ad-jacent to themagneti'cfsensitiye head. The support provides la imoving :surface iin engagement 'with tthe frecording member and moves .iialong :therewith fat .the same :rate :of speed. :Referring -to ."Fi'gs. 'i to the :recording .member -or wire :indicated 'at .Bllandiis taken oif ithefreel 32 "and wound on 4the l:rcel v'34. Vv`In`terirlediatefthe reels is fa 'cylindrical member or lcapstan tt. fixed 4`on -a1s'haiftl3'8 .to which ya driven :sheave` wheel "4m issecured yIn the illustrated embodiment i'of the invention fthe latter is approximately 'twice @the ldiameter of :the capstan, but itis yunderstood fthe dimensions 'of 'the l'two members may lbe yar-led to suit different conditions. .The fsheavew-he'el 4t is operatively coupled Ate :a drive pulley or sheave Wheel 42 by means of the endless belt 44. The driving sheave wheel 42` is iixed to a drive shaft 46 'of ya 1source of power `such 'as the 'elect-ric motor 48.

A ,magnetic sensitive soundhead of any sui-table conventional type is indicated at iii! sil-perimposing the capstan and resting lightlyV on the recording member which in turn rests on fthe peripheral surface of the capstan. The .head lis f carried von one end oi 4a lateral extending a'rin @52, whichhas its opposite end .pivoted atti yto an vupright post 5B. Vfielding-ly bearing against the opposite sides of the capstan are two idling wheels '3-'58 of similar construction which are free to rotate. Preferably these wheels engage the `fc'apstan below the axiswof rotation thereof as shown :in Fig. 1 and in such .a relation to the capstan that a line extending v.from the vcapstans axis to either axis of rotation of the idling wheels subtends an angle of approximately 45 to the vertical. The wire 3i! is led under each idling wheel FaS-58 and over the capstan and follows a path of movement indicated by the arrows in Fig. 1.

To preclude the possibility of developing eddy currents in the capstan, it is highly desirable to form the capstan out of insulating material such as a plastic compound, glass, et cetera. This is especially true when the device is used during the recording operation. The idling wheels are preferably constructed with a peripheral portion formed of a yieldable plastic or rubber. As shown in Fig. 1 each wheel is provided with a surface portion 5t. In addition to being free to rotate, each idling wheel 58-58 is mounted for bodily movement toward and away from the capstan. Each wheel is journaled by bearings or the like about a shaft t2. Each shaft is secured to the upper end of an arm 64 which is swingable toward and away from the capstan. The lower end of each arm is journaled by bearings or the like to a xed pivot pin 58 located inwardly of the axis of rotation of its respective wheel axis. The arms 64--64 are yieldingly urged toward one another to carry the wheels into engagement with the capstan by any suitable means such as the tensioned coiled spring 63 connected to both arms above their pivotal axes. it is evident that the spring yieldingly urges the resilient surface por tions of the idling wheels into yielding contact with the rim of the capstan.

The various parts of the apparatus may be mounted in any suitable way. As shown, the

parts are suppcrtingly mounted to form a unitary assembly. The supporting means comprises a relatively wide base 'I0 adjacent to the opposite ends of which the reels 32 and 34 are mounted by means of corresponding U-shaped brackets 'l2-J4 respectively. Each reel is i'lxed to a shaft which is rotatably ,oumaled l.fin y'the upright farms `@er thebracket. '.The shatgfor 'the take-oireel1is indicated etat; thelshafft .for the take-'on reel .is indicate-d at i8. latterfmayproieetreae werdlyas vsharm in 1e and be `provided with any; suitable conventionalfmeansfiorrotatingathe shaft ifrom the 'power sourcefand ior reciprocating .the-shaft andrea sziback andfforth morder to lay the A*Wire "evenly f. tai'Olllltl the '.'Spelmiposing the base is a blcekriB-D, the 'front `side yof which is divided into twofsurface :sections `B2 and im inniirerent vertical planes. The: motor #la is mounted onvthe-'top :of Vthe block. The post 56 'may ce" ink he forni faire metal strip secured at itsficwerenn 'to tinev iront sections: tor :the block and `'ogged intermediate lits iengtnat 86 :to .pre-

dispese the arma in alignment .with'the capstan es. The shaft 13e npo'n wllrchltne capstan and sheave wheel 4u `arecarried isniounted in an upright supporting member 88, thelewer end 'of which is secured to the top of the block' 89.. The tufo shafts S-56 about'whi'ch thezarms 64-64 pivot-:are fsupport'inglymounted in the :block and project .forwardly from meurent section e4.

The vwire 30 is 'properly directed under the first idling wheel-55's by means of a 'guiding device comprising'two parallel closely :extending cylinh ldricalf'members'or rodsiaweiwfshown in detail in Fig. 3. The 'wire .sas shown inFig. 3 is .led between 'the two .rods and regardless 'of 'what peripheral pci-tion ci the reelczfchewire is taken oif Zit .is "fed to the rst idlingwheelhlong :a predetermined liine. The two rods 'fare spaced apart "from eine another a cistanceslightly "greater than thediailneter of the wire forderte 'allow it 'to run freely therebetween. A spacer 92 may be used for this purpose. The two rods are mounted on a bracket 94 which in turn is secured to the iront section 82 of the supporting block 80.

Fig. 4 represents an enlarged detail sectional view through the magnetic head 5U showing its relation to the periphery of the capstan 35 and the wire 3i! supported thereby. The magnetic head may be any conventional or suitable type and its particular construction has no reference to the present invention. As shown in Fig. 4, the head comprises two complementary wall members Sii-95 supporting a horseshoe type of magnet 98 therebetween. The open ends of the magnet are very slightly spaced apart as is the conventional practice and they are grooved tangentially to provide a track for the recording wire to run therethrough as shown in Fig. 4. An important feature of the present invention is the fact that the section of the wire passing by the magnetic head is supported by a moving surface such as the periphery of the capstan which travels at the same speed as the wire. Moreover, for a considerable distance on either side of the head, the wire is in relatively tight engagement with the supporting surface represented by the capstan thereby frictionally holding this portion of the wire against elastical or vibratory movement. In the illustrated embodiment of the invention, the wire is held tightly against a peripheral portion of the capstan amounting to approximately 270 of its circular extent. The head is disposed in magnetic relation to the wire approximately midway between these two limits. Therefore, kfor that portion of the length of the wire immediately adjacent to the magnetic head, any stretching or contraction of the wire resulting from tension created by any non-uniform stationary or moving part of the apparatus is substantially dampened' out 'before it reaches that portion of the Wire in the vicinity of the head. The length of wire in contact with the capstan is determined by the smoothness of operation of .the parts preceding and following the capstan. lThis distance should be sucient to prevent substantially all variable or fluctuating elongation and contraction of the wire. A drum or capstan of 3% inch diameter-has been found to be highly desirable for this purpose.

I have found that it is also desirable, if the 'magnetic heads employed are microphonic, that is, ,act to transmit mechanical vibrations into electrical impulses, to solidly impregnate the head with an electrical and vibrational insulation materal such as asphalt. Lubricant between the wire and the head is helpful but a solidly irnpregnated body of asphaltum material both inside and outside the magnetic head produces better results.

What I claim is:

In a magnetic recording or play-back apparatus, supply means for supporting a quantity of resilient, longitudinally stretchable, elongated record element, take-up means for receiving the record element from said supply means, a capstan, means for driving the capstan, a rst roller intermediate said supply means and said capstan, a second roller intermediate said take-up means and said capstan, said rollers having surface portions formed of yieldable material in pressure contact with circumferentially spaced parts of the surface of said capstan, said record element extending from said supply means to and partly around said rst roller, thence around that portion of said capstan intermediate its circumferentially spaced surface parts in contact With said rolls, thence partly around said second roll and thence to said take-up means, a 1sound head positioned to engage that portion of the record element on the surface of said capstan midway between said rolls, said rolls being operative to absorb the energy of vibrational and other axial expansion and contraction originat- :ing in the portions thereof intermediate said supply and take-up means and the roller-s adjacent thereto and to isolate the portions of the record element in contact with the surface of said capstan from the -portions between said capstan and said supply and take-up means,

LAWRENCE H. CONNELL.

References Cited in the le of this patent UNITED STATES PATENTS Number Name Date 1,713,726 Vogt et al May 21, 1929 1,920,789 Heisler Aug. 1, 1933 2,237,738 Kuhlk Apr. 8, 1941 2,238,412 Daniel Apr. 15, 1941 2,251,322 Buhrendorf Aug. 5, 1941 2,349,018 Tasker May 16, 1944 2,418,543 Camras Apr. 8, 1947 2,468,198 Heller Apr. 26, 1949 FOREIGN PATENTS Number Country Date 4,933 Australia Nov. 26, 1926 606,631 Germany Oct. 25, 1934 

